- buy an at-the-money option expiring in the current week on a liquid etf. i like spy but qqq and iwm work just as well.
- after your purchase, send a gtc limit order to sell at a 50% gain.
- sell at the end of the day if the position still exists.
optional intraday adjustment: if the option drops 30% from the entry price then lower the asking price on the limit order to the break-even price (net of commissions.) a scratched trade is not a losing trade. however, i recommend not watching how the sausage is made, at least some of the time.
update 2/16/2013 - a small variation of this technique can convert this into an effective swing trading strategy. buy the option early in the week and if it does not hit the target price then simply let it ride. the market action dominates theta decay in these soon-to-expire options (a.k.a. gamma scalping.) the trick is to be trading small enough that the full loss is a normal acceptable loss.